This invention relates to a method and an apparatus for analyzing a liquid sample, and more particularly to a method and an apparatus suitable for analysis of a desired component in a liquid sample by adding a reagent to a liquid sample, thereby initiating reaction, and measuring the rate of reaction.
According to the conventional method and apparatus for analyzing a liquid sample by measuring the rate of the reaction, the physical quantity of reacting mixture is measured only after all the reagent has been added to a sample. In the measurement of the rate of reaction, a change in physical quantity per unit time is measured, but in the case of a sample with a very high activity, the reaction proceeds at a very high rate, so that there may be no more substrate as a reactant at the timing of actual measurement and thus there is no more change in physical quantity. That is, an analysis value corresponding to that of a sample with a low activity is obtained.
Thus, in the measurement of the rate of reaction an effective limit level is set for measuring the physical quantity, so that an alarm flag can be displayed to indicate that the analysis of the liquid sample is no more effective, as soon as the physical quantity becomes less than the effective limit level if a reactant in the reaction is taken into account (substrate basis) or as soon as the physical quantity becomes more than the effective limit level if a product in the reaction is taken into account (product basis). However, the conventional method and apparatus have problems in complete functioning of the alarm system.
According to the conventional method and apparatus, the measurement is carried out only after all the reagent has been added to a liquid sample to initiate reaction, and thus the effective limit level is set equally for all the samples. Thus, there is such a problem that no alarm flag is displayed when a sample with an unexpectedly large change in the physical quantity is involved. For example, analysis of glutamate-oxalacetate transminase (GOT) in serum, which is widely carried out in hospital laboratories, is carried out according to the following reactions (1) and (2): ##STR1##
When an absorbance is measured at the wave length of 340 nm, a change in NADH can be traced, and consequently, the rate of reaction (1) by GOT can be determined in conjugation with reaction (2), wherein MDH stands for malate dehydrogenase, NADH for reduced nicotinamide adenine dinucleotide, and NDA for nocotinamide adenine dinucleotide.
Analytical items usually inspected in hospitals by measuring changes in NADH at the wave length of 340 nm include amylase, creatine phosphokinase, glucose, glutamate-pyruvate transminase (GPT), .beta.-hydroxybutyrate dehydrogenase, lactate dehydrogenase (LDH), triglyceride, urea nitrogen, etc. However, absorbance at the wave length of 340 nm of serum as samples for analyzing these analytical items in hospital laboratories has some distribution. In FIG. 1, distribution of absorbance of 13-fold diluted serum samples of 200 patients in a hospital is shown. As is seen therefrom, the absorbance at the wave length of 340 nm has a large deviation depending upon the individual patients. Thus, the conventional method and apparatus based on the effective limit level being set by disregarding such a large deviation in the absorbance of serum have such a disadvantage that the alarm flag sometimes fails to function.